This application claims the priority of Korean Patent Application No. 2002-18026, filed Apr. 2, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method for fabricating a metal oxide thin film by using a chemical vapor deposition method or atomic layer deposition method, and more particularly, to a method for fabricating a metal oxide thin film by using a chemical vapor deposition method or an atomic layer deposition method which uses alcohol vapor as a reactant gas.
2. Description of the Related Art
A chemical vapor deposition method is widely used for forming oxides, nitrides and sulfides of a metal, and metallic thin films. It is also used for forming a polymer or organic thin film. Since thin films fabricated by the chemical vapor deposition method have a characteristic of uniform step coverage in a three-dimensional structure, the chemical vapor deposition is extensively used as a fabrication method of highly integrated devices, particularly, in the semiconductor field.
Also, researchers are actively studying on an atomic layer deposition method, which is an advanced form of the chemical vapor deposition, for fabrication of ultra-thin films because perfect step coverage can be obtained from the method, even though there is a shortcoming of slow deposition rate [Nanotechnology 10, pp. 19–24, 1999; and U.S. Pat. No. 4,058,430].
In general, multi-component oxide films, such as BST, STO and PZT, are fabricated by decomposing a precursor in the form of a metal-organic compound comprising metal ions and ligands. The most popular ligands are of β-diketone group [Materials Science Forum Vol. 137–139, pp.473–494, 1993]. As for reactant gases to decompose them, oxygen-containing gases such as oxygen (O2) and ozone have been mostly used [Chem. Vap. Deposition 7, pp.146–149, 2001; and Integrated Ferroelectrics 30, pp.45–52, 2000]
However, the oxygen-containing gases have a shortcoming of forming a second oxide layer, because they oxidize the deposition surface as well as the precursor. For example, when an oxide film is formed on silicon, which is quick to be oxidized, by using an oxygen-containing gas, a second oxide film is formed between the silicon and the oxide film [Jpn. J. Appl. Phys. 37, pp.3396–3401, 1998; and Chem. Mater. 13, pp.2463–2464, 2001].
Recently, many researchers are studying on the atomic layer deposition of a metal oxide film by using a metal-organic precursor. Here, H2O, which is usually used in this process, hinders a process control, because once H2O is adsorbed into vacuum equipment during process, it is hardly removed [Materials Science and Engineering B41, pp.23–29, 1996].
Besides, since the atomic layer deposition is a method that forms a thin film by the surface reaction between the precursors adsorbed on the surface and the reactant gas, precursors with high reactivity, such as cyclopentadienyl group, alkoxide group or halide group are required necessarily [Science 288, pp.319–321, 2000].
However, as those precursors with high reactivity have a low chemical and thermal stability, it is difficult to secure reproductivity and reliability in the deposition process. On the other hand, precursors of β-diketone group have a relatively excellent chemical, thermal stability, but too low reactivity to be used in the atomic layer deposition. Thus, in order to activate surface reaction, deposition temperature should be raised, or gases with high reactivity such as ozone should be used. Otherwise, plasma-enhanced atomic layer deposition (PEALD) method using plasma should be used [J. Mater. Chem. 7, pp.449–454, 1997; and Korean patent application laid-open publication No. 2000-0049298].